Our apartment is surrounded by silver and red maples, which are home to several families of squirrels, both black and grey. They bury maple keys and sunflower seeds in my containers every fall and then proceed to dig them up every sping. They seem to know when soil has been worked and until I started protecting my containers, they would dig up any seeds I'd sown and even small transplants. Even sprinkling bloodmeal around my plants didn't deter them. Now I use physical barriers - bamboo stakes, screening, and the presence of our two Siamese, Meng & Puff, to keep my plant babies safe!